The invention relates to a high-speed rotary atomizer for applying powder coating, with a housing; with a rotatable bell-shaped plate which is disposed at the front of the housing; with a motor which is accommodated in the housing and drives the bell-shaped plate, and with at least one powder supply duct which extends through the housing and emerges at the front of the housing.
The powder supply duct of known high-speed rotary atomizers of this type which are currently on the market leads through the hollow shaft of the motor and opens out at the front very near the axis of the bell-shaped plate. This arrangement entails two disadvantages: Firstly, the cross section of the powder supply duct may only be relatively small, which limits the powder throughput and thus the coating performance of the high-speed rotary atomizer. Secondly, the coating powder is brought into the range of action of the high-speed rotary atomizer very near the axis, where the speed of the atomizer is relatively low. This impairs the efficiency of the vorticity which is achieved by the bell-shaped plate.
The object of the invention is to provide a high-speed rotary atomizer of the type initially mentioned whose coating performance is significantly better.
This object is achieved according to the invention in that the powder supply duct leads through the housing radially outside of the motor.
Therefore, according to the invention, the supply of powder to the bell-shaped plate through the housing no longer takes place through the hollow shaft of the motor. The entire motor is instead xe2x80x9cbypassedxe2x80x9d by the powder supply duct. The duct may thus be laid through a region of the housing in which there is sufficient space for large cross sections. The powder throughput is therefore no longer limited by geometric conditions.
The configuration according to the invention may also comprise a plurality of powder supply ducts without any problems. It is in this case particularly advisable to provide a configuration in which a plurality of powder supply ducts are disposed radially outside of the motor in corresponding multidentate rotational symmetry. This achieves not just a very high powder throughput, but also very satisfactory homogeneity of the powder cloud which is produced.
The powder supply duct may be formed at the interface between two parts, at least in one portion. The advantage of this lies in the fact that the inner surface of this region of the powder supply duct is immediately accessible and can be cleaned when the two parts are disassembled.
It is in this respect particularly preferable for the two said parts to be the housing on the one hand and a housing insert on the other.
The use of high-speed rotary atomizers with so-called xe2x80x9cinternal chargingxe2x80x9d has recently increased. This term means that the high-voltage electrode by means of which the powder coating particles are ionized is located inside the housing of the high-speed rotary atomizer.
xe2x80x9cInternal chargingxe2x80x9d is contrary to xe2x80x9cexternal chargingxe2x80x9d, where the high-voltage electrode is generally provided as a ring, which surrounds the bell-shaped plate, outside of the housing. In the case of xe2x80x9cexternal chargingxe2x80x9d, the air surrounding the outer electrode is firstly ionized, after which the coating powder is indirectly ionized via the latter, this having a relatively poor efficiency. In the case of xe2x80x9cinternal chargingxe2x80x9d, however, the coating powder particles are ionized through direct contact with the high-voltage electrode, this taking place more efficiently.
If, therefore, the inventive concept is employed with high-speed rotary atomizers with internal charging, it is particularly advantageous to connect the housing insert, which partly defines the powder supply duct, as a high-voltage electrode. The coating powder is thus brought over a considerable distance through the housing into contact with a surface carrying a high voltage. This results in a very good ionization effect.
The housing and at least one housing insert may be of a conical formation in the front region and lie against one another with cone faces. This mechanical structure facilitates assembly and disassembly of the high-speed rotary atomizer, as the housing and the housing insert can be fixed in one direction by fitting the conical regions into one another and only require a fastening device at the opposite end.
It is preferable in this case for the cone faces of the housing and of the housing insert to be self-sealing and/or self-locking. This also facilitates assembly; special sealing means are unnecessary.
The shaft of the motor which drives the bell-shaped plate generally has air bearings. An air bearing bush, in which the shaft of the motor is guided, is provided for this purpose. Bearing air is forced radially inwards through small ducts in the air bearing bush and thus forms an air cushion between the inner surface area of the air bearing bush and the outer surface area of the shaft. If an air bearing arrangement of this kind is used in the present invention, it is particularly advantageous for the shaft of the motor to be hollow and comprise radial bores via which the bearing air can pass into the interior space of the shaft, and for the interior space of the shaft to communicate with a through-bore in the bell-shaped plate which opens into the end side of the bell-shaped plate. According to the invention, the shaft is no longer required for supplying powder; it can now be used for other purposes, i.e. for supplying cleaning air to the bell-shaped plate for blowing off adhesions at this point. In this configuration of the invention the bearing air is supplied for a second purpose: Because it can enter the hollow shaft of the motor and be supplied via this to the bell-shaped plate, it does not emerge unused, as was previously the case, instead additionally performing the cleaning function.